As shown in FIG. 15, a steering apparatus for an automobile is configured such that rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, a pair of left and right tie-rods 4, 4 is pushed/pulled in connection with rotation of the input shaft 3 and a steering angle is thus applied to front wheels. The steering wheel 1 is supported and fixed to a rear end portion of a steering shaft 5. The steering shaft 5 is rotatably supported to a cylindrical steering column 6 with being axially inserted into the steering column 6. A front end portion of the steering column 6 is connected and fixed to a rear end portion of a housing 9 in which a worm decelerator 7, a torque measuring device 8 (see FIG. 16) and the like configuring an electric power steering apparatus are accommodated. An electric motor 10 that is a power source of the electric power steering apparatus is supported and fixed to the housing 9.
When the steering shaft 5 is rotated by the steering wheel 1, a direction and amplitude of torque applied to the steering shaft 5 are measured by the torque measuring device 8. The torque measuring device 8 has an input shaft 12, an output shaft 13 and a displacement measuring device 14 (see FIG. 16) that is configured to measure a relative displacement amount as regards a rotating direction between the input shaft 12 and the output shaft 13. The input shaft 12 and the output shaft 13 are rotatably supported in the housing 9 and are connected to each other by a torsion bar 11. Since the configuration and operation of the torque measuring device 8 are well known, the detailed descriptions thereof are omitted. Based on a measurement result of the torque measuring device 8, the electric motor 10 applies auxiliary torque to the output shaft 13 in the same direction as the operation direction of the steering wheel 1, thereby rotating the output shaft 13 with torque larger than the torque input to the input shaft 12 from the steering shaft 5.
A front end portion of the output shaft 13 is coupled to a rear end portion of an intermediate shaft 16 via a universal joint 15a. A front end portion of the intermediate shaft 16 is coupled to the input shaft 3 via a separate universal joint 15b. In the specification, a front-rear direction is a front-rear direction of a vehicle in a state in which the electric power steering apparatus is mounted on the vehicle, and also includes an inclined case relative to a horizontal direction. A tilt mechanism configured to adjust an upper-lower position of the steering wheel 1 and a telescopic mechanism configured to adjust a front-rear position thereof are mounted to the steering apparatus for an automobile shown in FIG. 15. An intermediate portion of the steering column 6 is supported to a support bracket 18 supported to a vehicle body 17 so that an upper-lower position and a front-rear position thereof can be adjusted. In order to configure the tilt mechanism, a support cylinder 19 is provided at a front-upper end portion of the housing 9 and is supported to the vehicle body 17 so that it can be swing-displaced about a horizontal axis. In order to configure the telescopic mechanism, the steering shaft 5 has an inner shaft and an outer shaft that are combined to transmit the torque and to be expandable and contractible, and the steering column 6 has an outer column and an inner column that are combined to be expandable and contractible.
As a more specific structure of the electric power steering apparatus as described above, FIG. 16 shows a structure disclosed in Patent Document 1 and FIG. 17 shows a structure disclosed in Patent Document 2. First, in the structure shown in FIG. 16, a housing 9a for accommodating components except for the electric motor 10 (see FIG. 15) of the electric power steering apparatus is configured by combining a gear housing 20 and a housing cover 21. The output shaft 13 is rotatably supported in the housing 9a by a front-side rolling bearing 22 that is held on an inner peripheral surface of a front end portion of the gear housing 20 and a rear-side rolling bearing 23 that is held on an inner peripheral surface of a front end portion of the housing cover 21. The input shaft 12 is rotatably supported in the housing cover 21 by a separate rolling bearing 24 (a radial needle bearing) that is held on an inner peripheral surface of an intermediate portion of the housing cover 21.
In the structure shown in FIG. 17, a partition plate 25 is fitted at a portion of an inner side of a gear housing 20a near the rear end. An elastic material 26 is interposed between an outer peripheral surface of the partition plate 25 and an inner peripheral surface of the gear housing 20a. An output shaft 13a is rotatably supported in the housing 9a by a front-side rolling bearing 22a that is held on an inner peripheral surface of a front end portion of the gear housing 20a and a rear-side rolling bearing 23a that is held on an inner peripheral surface of the partition plate 25. An input shaft 12a is rotatably supported in a housing cover 21a by a separate rolling bearing 24a. Since the structure shown in FIG. 17 does not have a telescopic mechanism, both a steering shaft 5a and a steering column 6a are not a telescopic type.
In the structure shown in FIG. 16, the housing 9a is configured by combining the gear housing 20 and the housing cover 21 and the output shaft 13 is rotatably supported in the housing 9a by the front-side rolling bearing 22 and the rear-side rolling bearing 23. The corresponding operations are troublesome, so that manufacturing efficiency of the electric power steering apparatus is lowered.
In contrast, in the structure shown in FIG. 17, there is no troublesome assembling operation as described above. However, it is difficult to maintain positioning precision of the output shaft 13a for a long time. That is, when the elastic material 26 provided between the outer peripheral surface of the partition plate 25 and the inner peripheral surface of the gear housing 20a is deteriorated due to longtime using and the elasticity thereof is thus lowered, the partition plate 25 may slip. When the partition plate 25 slips, an engaging resistance between a worm and a worm wheel of the worm decelerator 7a is increased or the detection precision of the torque measuring device 8a is degraded, which lowers the performance of the electric power steering apparatus.